On the website
http://www.airtran.com/programs/aplus/amex.jsp
it says,
"Or take three roundtrips in Business Class, or six roundtrips in coach, and AirTran
Airways will buy you a free roundtrip coach ticket on any major airline to places we
don't fly in the continental U.S."
Skimming the fine print it looks like all flights are from Atlanta.
"Free Flights on Other Airlines: Two A-Plus Travel Reward Certificates (24 Flight Credit Vouchers) are required for one free coach
roundtrip ticket for travel between Atlanta (ATL) and any point in the 48 continental United States served nonstop (no connections) or direct (one-stop). You must agree to fly on one of the following carriers: American, America West, ATA, Atlantic Southeast Airlines, Continental, Delta, MetroJet, Midway, Midwest Express, Northwest, TWA, United or US Airways. All flights on airlines other than AirTran Airways must originate from and return to Atlanta. Travel to/from Atlanta is the sole responsibility of the recipient. Free travel on other airlines is available only on nonstop and direct (one-stop) flights from Atlanta. Free travel on other airlines will not be issued on
routes where AirTran Airways publishes schedules and fares. On those routes, free tickets will be issued for AirTran Airways flights for one A-Plus Travel Reward Certificate (12 Flight Credit Vouchers)."